31745

سنتز و بررسي خواص جذب امواج الكترومغناطيسي نانوساختار هسته¬پوسته فريت كبالت، اكسيد روي، كربن

كارشناسي ارشد

نانوفناوري

1400

1403/07/15

دكتر ميثم جلالي

دكتر ميثم جلالي

فناوري هاي نوين

در سال¬هاي اخير با توجه به فراگيري تكنولوژي، گستره¬ي استفاده از امواج الكترومغناطيسي به طور وسيعي در زمينه¬هاي مختلف رشد كرده¬است. علاوه بر مزاياي فراوان امواج الكترومغناطيسي، مخاطرات و تهديداتي نيز وجود دارد كه با توليد مواد جاذب امواج الكترومغناطيسي و استفاده در پوشش¬هاي ضدتداخل امواج الكترومغناطيسي، تكنولوژي استتار و محافظ¬هاي بيولوژيكي مي¬توان از آن¬ها جلوگيري كرد. در پژوهش كنوني به منظور دست¬يابي به يك ماده¬ي جاذب امواج الكترومغناطيسي با حداقل 90% جذب انرژي امواج، با توجه به مكانيسم¬هاي اتلاف مواد مغناطيسي و دي¬الكتريك و عوامل تاثيرگذار بر جذب همچون نوع ماده، اندازه ذره و ساختار، نانوذرات هسته-پوسته CoFe2O4@ZnO@C در طي سه مرحله به روش هم¬رسوبي و هيدروترمال و فرايندهاي تكميلي همچون كلسيناسيون و پيروليز سنتز شدند. پارافين به عنوان بستر پليمري و نسبت 1:1 به عنوان نسبت پودر به بستر تعيين شد. ابتدا بسترپليمري خالص و همچنين نمونه حاوي نانوذرات فريت كبالت مورد بررسي خواص جذبي قرار گرفت و به ترتيب داراي اتلاف بازگشتي -2/3 dB در فركانس 10/15 GHz و -4/7 dB در فركانس 9/65 GHz بودند.با مشخص شدن سهم زمينه و نانوذرات فريت كبالت در جذب، نمونه¬هاي نانوكامپوزيتي با استفاده از نانوذرات CoFe2O4@ZnO با پنج نسبت مختلف اعم از 1:3، 1:2، 1:1، 2:1 و 3:1 با ضخامت 3 mm سنتز شدند و نتايج خواص جذبي آن¬ها مورد بررسي قرار گرفت. نانوذرات CoFe2O4@ZnO با نسبت 2:1 با كسب بيشترين اتلاف بازگشتي به ميزان -6/5 dB در فركانس 10/6 GHz به عنوان نسبت بهينه نانوساختار دوجزئي تعيين شد. نمونه¬هاي حاوي نانوذرات CoFe2O4@ZnO@C پس از اختلاط در بستر پارافيني با نسبت 1:1 و ضخامت¬هاي 0/5 ، 1 ، 1/5 ، 2 ، 2/5 ، و 3 mm توليد شدند. از ميان نمونه¬هاي بررسي شده در اين تحقيق، نمونه¬ با ضخامت 0/5 mm با دارا بودن تلفات دي-الكتريك ناشي از حضور كربن و اكسيدروي و تلفات مغناطيسي ناشي از فريت كبالت در طول باند X، موفق به جذب 97% از انرژي موج با رسيدن به اتلاف بازتابي به مقدار -20 dB در فركانس¬هاي 8/2 GHz و 10/3 GHz با پهناي باند كامل در باند X شد. مهم ترين عامل ميزان جذب كسب شده، در وهله¬ي اول به تطابق امپدانس در ضخامت 0/5 mm و مكانيسم¬هاي اتلافي همچون رزونانس طبيعي به دليل وجود فريت كبالت، اتلاف جريان گردابي به دليل ضخامت مناسب نمونه، اتلاف پلاريزاسيون (قطبش دوقطبي و سطحي) به دليل وجود فصل مشترك دي¬الكتريك-مغناطيسي ناشي از ساختار هسته-نسبت داده شد.

1403/09/21

Synthesis and investigation of electromagnetic waves absorption properties of core-shell nanostructured cobalt ferrite, zinc oxide, carbon

10/6/2025 12:00:00 AM

In recent years, due to the spread of technology, the scope of using electromagnetic waves has grown widely in various fields. In addition to the many benefits of electromagnetic waves, there are also dangers and threats that can be avoided by producing electromagnetic wave absorbing materials and using electromagnetic wave anti-interference coatings, camouflage technology, biological protectors, etc. In the current research, in order to achieve an electromagnetic wave absorbing material with at least %90 wave energy absorption, considering the loss mechanisms of magnetic and dielectric materials and factors affecting absorption such as the type of material, particle size and structure. CoFe2O4@ZnO@C core-shell nanoparticles were synthesized in three steps by co-precipitation and hydrothermal methods and additional processes such as calcination and pyrolysis. Paraffin was used as polymer substrate and 1:1 ratio was determined as powder to substrate ratio. First, the pure polymer substrate as well as the sample containing cobalt ferrite nanoparticles were investigated for absorption properties and they had return loss of -3.2 dB at 15.10 GHz frequency and -7.4 dB at 65.9 GHz frequency, respectively. The contribution of the background and cobalt ferrite nanoparticles in the absorption of nanocomposite samples using CoFe2O4@ZnO nanoparticles with five different ratios of 1:3, 1:2, 1:1, 2:1 and 3:1 with a thickness of 3 mm. the results of their absorption properties were investigated. CoFe2O4@ZnO nanoparticles with a ratio of 2:1 with the highest return loss of -5.6 dB at a frequency of 6.10 GHz was determined as the optimal ratio of the two-component nanostructure. Samples containing CoFe2O4@ZnO@C nanoparticles were produced after mixing in a paraffin with a ratio of 1:1 and thicknesses of 0.5, 1, 1.5, 2, 5.2, and 3 mm. Among the samples examined in this research, the sample with a thickness of 0.5 mm, having dielectric losses due to the presence of carbon and zinc oxide and magnetic losses due to cobalt ferrite along the X band, managed to absorb 97% of The wave energy reached the reflection loss of -20 dB at the frequencies of 2.8 GHz and 3.10 GHz with full bandwidth in the X band. The most important factor of the obtained absorption rate was attributed to the impedance matching in the thickness of 0.5 mm and then to the presence of carbon.

نانوكامپوزيت، امواج الكترومغناطيسي، اتلاف بازتاب، جذب، ساختار هسته-پوسته

In recent years, due to the spread of technology, the scope of using electromagnetic waves has grown widely in various fields. In addition to the many benefits of electromagnetic waves, there are also dangers and threats that can be avoided by producing electromagnetic wave absorbing materials and using electromagnetic wave anti-interference coatings, camouflage technology, biological protectors, etc. In the current research, in order to achieve an electromagnetic wave absorbing material with at least %90 wave energy absorption, considering the loss mechanisms of magnetic and dielectric materials and factors affecting absorption such as the type of material, particle size and structure. CoFe2O4@ZnO@C core-shell nanoparticles were synthesized in three steps by co-precipitation and hydrothermal methods and additional processes such as calcination and pyrolysis. Paraffin was used as polymer substrate and 1:1 ratio was determined as powder to substrate ratio. First, the pure polymer substrate as well as the sample containing cobalt ferrite nanoparticles were investigated for absorption properties and they had return loss of -3.2 dB at 15.10 GHz frequency and -7.4 dB at 65.9 GHz frequency, respectively. The contribution of the background and cobalt ferrite nanoparticles in the absorption of nanocomposite samples using CoFe2O4@ZnO nanoparticles with five different ratios of 1:3, 1:2, 1:1, 2:1 and 3:1 with a thickness of 3 mm. the results of their absorption properties were investigated. CoFe2O4@ZnO nanoparticles with a ratio of 2:1 with the highest return loss of -5.6 dB at a frequency of 6.10 GHz was determined as the optimal ratio of the two-component nanostructure. Samples containing CoFe2O4@ZnO@C nanoparticles were produced after mixing in a paraffin with a ratio of 1:1 and thicknesses of 0.5, 1, 1.5, 2, 5.2, and 3 mm. Among the samples examined in this research, the sample with a thickness of 0.5 mm, having dielectric losses due to the presence of carbon and zinc oxide and magnetic losses due to cobalt ferrite along the X band, managed to absorb 97% of The wave energy reached the reflection loss of -20 dB at the frequencies of 2.8 GHz and 3.10 GHz with full bandwidth in the X band. The most important factor of the obtained absorption rate was attributed to the impedance matching in the thickness of 0.5 mm and then to the presence of carbon.

Mohammad Khalesi Hamedani

Dr. Jalali